1. Field of the Invention
This invention relates to a memory circuit with auto redundancy, and more particularly to a circuit which includes the redundant memory cells to replace the defective memory cells in the user application situation.
2. Background of the Invention
It is desired for semiconductor memory chips to improve the "Yield". In general, the manufacturers use an additional redundant memory cells in the chips to improve the yield. The redundant memory cells are used to replace the defective cells prior to packaging. The redundancy technique is always used in the EPROM writer extensively. But this method is only for semiconductor manufacturers to repair the defective cells, it is not for the customer to use when the memory is invalid.
For understanding the conventional redundancy technique more detailed, we take a flow chart to describe the conventional redundancy shown as FIG. 1. In FIG. 1, at first, to set the address signal at the first location 201 after the program begins 200. Then, it sets programming mode and perform program writing (that is, program pulse 500uS) 203. Further, it judges the address signal is the last signal or not 204? If no, the address signal add 1 205 and back to perform program writing 203. If yes, the address signal points the first location 206, then the number of times will be N=0 207. The N means the times of verify program, and it can be set by the user. In this case, the N is set as 25. After setting the N=0, verify the writing data is failed or passed 208. If the data is fail(not correct), then set N=N+1 209. Furthermore, it judge the N=25 210? If N=25, then the device is failed 212. If N.noteq.25, it will be continued to perform program writing 211, and verify the data is failed or passed 208. On the other hand, if the result from the verify data is passed (after 208), then judge the address signal is the last signal or not 213. If not, the address signal will be add 1 214 and back to the set N=0 207. If the address signal is the last signal, then set the program in reading mode 215. Further, compare all data are failed or passed 216. If passed, the program is end 217. If failed, the all data in the program are failed and mean the device is failed 212.
In the conventional memory redundancy, there almost use the fuses as the redundancy cells. For example, the Poly-fuse and Metal-fuse are used as the redundancy material. It is a defect that the fuse (Poly-fuse, Metal-fuse) can only record one time. Furthermore, when the fuse be recorded, there always need another operation procedure. It can not use the electrically programmable read-only memories (EPROM.sub.-- cell), electrically erasable programmable read-only memories (EEPROM.sub.-- cell), and the flash memory (Flash.sub.-- cell) either. So the prior art is not convenient for user, especially about that the customer can not repair the defective memory cells in the prior art.
Thus, there still remains a need for a memory circuit with auto redundancy which overcomes the drawback of the conventional memory redundancy, and the memory circuit provides a convenient method for user to repair the defective memory cells automatically, and it can use the general memory cells to act the fuse cell.